“Are you sure you want to do this” is a hosting issue not a theme or WordPress one. Normally you can just choose an option to continue?
The FTP route - have you tried using FileZilla? Dreamweaver does not sound like the right way to do this.
FileZilla will give you the full installation (might be abides emit start a fresh) so you should just need to UNZIP the theme folder and drop it in the themes folder there